The use of the solid state in synthetic organic chemistry conveys enormous advantages in terms of separation and purification of materials, particularly in multistep syntheses. Starting with the synthesis of polypeptides and continuing with the synthesis of polynucleotides, attachment of substrates to a solid-material has enabled chemists to remove by-products and impurities readily over many high yield steps. The method has become a central feature in the synthesis of organic materials with repetitive units. The solid state also provides unique opportunities to control organic reactions.
Solid inorganic silicates that include clays and zeolites have provided a framework for separations and catalysis utilizing naturally occurring mesoporous cavities. The use of organics as templates has allowed such cavities to be created with designed shapes. Silicate cavities offer acidic and basic sites for interaction with guest molecules. Specially designed organic clathrates also can provide cavities or channels in which guests may reside. The insoluble nature of these mesoporous inorganic and organic hosts permits their use in heterogeneous contexts, whereby purifications (such as removal of water by molecular sieves) can be effected and the host and bound impurity removed by simple filtration.
Well-known organic hosts, in the art, include crown ethers, cyclodextrins, calixarenes, and spherands. These molecules usually are soluble in aqueous or organic solvents and serve as hosts for a wide variety of neutral organics, cations, and anions. Their uses now are legion, including drug delivery, catalysis, and purification. Cyclodextrins (abbreviated herein as CD) are cyclic oligomers of glucose, which possess a hydrophilic exterior and a hydrophobic interior into which a variety of small, usually neutral molecules may be introduced. Calixarenes (abbreviated herein as CX) are cyclic oligomers in which aligned phenols, connected by methylene units, serve to complex metals ions and other cations in particular. These hosts offer cavities on the nanometer scale, generally smaller than the zeolitic cavities. Moreover, in contrast to zeolites, CDs and CXs are usually handled in solution, and the host-guest interactions occur within the single liquid phase.
There are several reports in the prior art of insoluble versions of these organic hosts. Typically, the hosts are incorporated into polymers either by direct synthesis or by coating or grafting the host onto a stationary phase. In particular, CD was connected to urethane polymers to create highly cross-linked, insoluble materials, which they envisaged as useful for environmental separations. CD was also incorporated into prior art mesostructured silica noncovalently by co-condensation. CD units were also attached to insoluble organic polymers to create new drug delivery systems. There also have been several reports of insoluble CXs, immobilized noncovalently on organic supports such as polymer beads.